Marrellomorpha

Marrellomorpha are an extinct group of arthropods known from the Cambrian to the Early Devonian.[1] They lacked mineralised hard parts, so are only known from areas of exceptional preservation, limiting their fossil distribution. The best known member is Marrella, with thousands of specimens found in the Cambrian aged Burgess Shale of Canada. The group is divided up into two major orders, Marrellida and Acercostraca. Marrellida is recognised by the possession of head shields with two or three pairs of elongate spine-like projections, and three pairs of uniramous appendages on the cephalon, while Acercostraca generally have large ovoid carapaces that cover the entire upper half of the body, and five pairs of uniramous cephalic appendages. Both groups have unbranched antennules and a segmented trunk with biramous appendages.[2] Recent research has suggested the previously enigmatic Cambrian trilobite-like arthropods Skania and Primicaris belong to this group.[3][2] Their phylogenetic position is uncertain, various studies have alternatively placed them in the Arachnomorpha as relatives of Artiopoda (trilobites and kin), as related to Mandibulata, or as stem group euarthropods.[2]

Marrellomorpha
Temporal range:
Life restoration of Marrella from the Burgess Shale
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Marrellomorpha
Beurlen, 1930
Subgroups
  • Acercostraca
  • Marrellida

Taxonomy

After Moysiuk et al., 2022.[2]

Fragmentary taxa assigned to Marrellomorpha include Austromarrella from Cambrian Series 3 aged deposits in Australia,[4] and Dyrnwynia from the Ordovician (Darriwilian) aged Llanfallteg Formation of Wales, which in its original description was assigned to Marrelida.[5]

Phylogeny

After Legg, 2016.[6]

Outgroups

Marrellomorpha
Marrellida

Marrella splendens

Mimetasteridae

Furca bohemica

Moroccan marrellid

Mimetaster hexagonalis

Acercostraca

Skania fragilis

Primicaris larvaformis

"Skania" sundbergi

Vachonisiidae

Enosiaspis hrungnir

Xylokorys chledophilia

Vachonisia rogeri

After Moysiuk et al., 2022.[2]

Marrellomorpha
Marrellida

"Mimetaster" florestaensis

Furca bohemica

Mimetaster hexagonalis

Tomlinsonus dimitrii

Moroccan marrellid

Marrella

Palaeoisopus

Haliestes

Aquilonifer

Acercostraca

Vachonisia

Xylokorys

Enosiaspis

Skania

Primicaris

Eoredlichia

Mollisonia

Waptia

Tokummia

Kylinxia

Taxa usually not
considered marrellomorphs

References


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